Added 24bit RGB to 8bit greyscale transformation

src/ptbench/data/transforms.py

@@ -41,6 +41,29 @@ class SingleAutoLevel16to8:
             ).astype("uint8"),
         ).convert("L")
 
+class RGBtoGreyscale8bit:
+    """Converts a 24-bit RGB image to an 8-bit greyscale representation.
+    
+    This transform assumes that the input image is RGB with 24 bits.
+
+    Converts the RGB image to a greyscale image using the well-known formula:
+    Y = 0.299 * R + 0.587 * G + 0.114 * B
+    This formula is based on the relative luminance of the RGB channels in the sRGB color space
+    
+    consider such a range should be mapped to the [0,255] range of the
+    destination image.
+    """
+
+    def __call__(self, img):
+        # Use the formula to convert the RGB image to a greyscale image
+        img_array = numpy.array(img).astype(float)
+        grey_array = 0.299 * img_array[:, :, 0] + 0.587 * img_array[:, :, 1] + 0.114 * img_array[:, :, 2]
+        
+        # Normalize the greyscale image to the range [0, 255] and convert it to uint8
+        grey_array = numpy.round(255.0 * (grey_array - grey_array.min()) / (grey_array.max() - grey_array.min())).astype('uint8')
+        
+        # Create a new greyscale PIL image from the normalized array
+        return PIL.Image.fromarray(grey_array).convert("L")
 
 class RemoveBlackBorders:
     """Remove black borders of CXR."""